The production of streptomycin is limited mostly to a few strains of Streptomyces griseus (Schatz, Bugie, and Waksman, 1944; Waksman, Reilly, and Johnstone, 1946; Carvajal, 1946a and b) and to Streptomyces bikiniensis (Johnstone and Waksman, 1948). Trussell, Fulton, and Grant (1947) examined a strain of Streptomyces which appeared to produce both streptomycin and streptothricin. Although this organism resembled Streptomyces lavendulae, it possessed morphological and biochemical characteristics that differentiated it from the described species. More recently, Benedict et al. (1950) reported that a strain of Streptomyces griseocarneus nov. sp. produced a closely related member of the streptomycin series, hydroxystreptomycin, which differed from streptomycin only in having a hydroxymethyl group instead of a methyl group in the streptose portion of the molecule. From a strain of Streptomyces similar to, but not identical with, S. griseocarneus, Grundy et al. (1950) isolated and characterized an antibiotic identical with hydroxystreptomycin. The purpose of this paper is (1) to provide a detailed morphological and physiological description of S. griseocarneus as stipulated by Benedict et al. (1950), and (2) to report studies on the production of hydroxystreptomycin by this organism in laboratory and pilot-plant scale fermentation and to consider other factors encountered in this work. EXPERIMENTAL METHODS AND RESULTS